Precision shape adjustment is a fabrication procedure with a particular need for ongoing improvement because of its use in the processing of numerous small, high-precision objects. Solid structures with a need for precision shape adjustment are for instance the sliders in hard disk drives. Sliders are manufactured to narrow dimensional tolerances, in particular at their air-bearing surface.
The air-bearing surface is designed to keep the magnetic recording head at a predetermined flying height above the rotating disk during its read and write operation. The flying height influences the achievable data storage density on the rotating disk. In order to increase storage density, the air-bearing surface must be designed to allow smaller and smaller flying heights.
The continuous miniaturization of sliders makes it increasingly more difficult to control their ever-tighter shape tolerances. Slider shape deficiencies that result from conventional manufacturing techniques become more critical for the operational performance of the slider on a disk, during contact start stop (CSS) and/or during slider load/unload operations.
Commonly, a lapping process is used that induces surface stress on selected regions or faces of the magnetic recording sliders and performs microscopic dimensional shape adjustment. The lapping process is typically carried out at the slider row level. Hence, it provides a very limited possibility to adjust individual magnetic recording heads. Further, the lapping process becomes more difficult to apply as the desired tolerances of the produced sliders become smaller.
The fabrication methods, used to create and smooth the microscopic air-bearing surface, typically generate flat, sharp edged features and contours. As an unfavorable result, air-bearing edges and corners, which occasionally come into contact with the disk, become more likely to penetrate lubrication and wear layers on the disk and scratch the magnetic layers of the hard disk. To address this problem, fabrication techniques are introduced at a late stage of the manufacturing process to induce a convex curvature to the air-bearing surface. This curvature prevents on one hand areal surface contact and stiction between the slider and the disk surface. On the other hand, the induced curvature reduces the risk of cutting or abrading the disc surface with the air-bearing surface during dynamic contact.
One fabrication technique used to induce surface curvature is known as scribing. It is described in the U.S. Pat. No. 5,704,112. The patent describes a method for mechanically forming grooves in the material on areas of the air-bearing surface. The grooves are preferably created by a diamond tip that is moved with a small load along a surface of the work piece. The description is indefinite as to how far the removal of material will enable bending of the slider by changing the stress induced on that side of the slider during its prior polishing. The use of a diamond tool with an edge angle of 120 degrees and a load of 100/150 gr is disclosed in FIGS. 9 and 10. It is known to those skilled in the art that the use of such a tool in combination with materials used for the manufacturing of sliders causes at least some plastic deformation together with the removal of material. The inducement of plastic deformation is the source of compressive strain in the area surrounding the grooves. To the contrary, column 4, line 47 and following describe in an embodiment alternative creation of the grooves as shown in FIG. 3. The use of many very different material removal techniques is listed without identifying their influence on creating compressive strain.
Mechanical scribing by the use of a diamond tool requires very high precision; it is time consuming and expensive for mass production. The application of adequate gram loads on the microscopic work pieces is also problematic, because it requires additional mechanical support for the work piece. Grooved surfaces have to be accessible for the diamond tool, which puts a limitation on the design of the air-bearing surface.
Another shortcoming of mechanical scribing is the unavoidable creation of microscopic debris. Microscopic debris makes additional cleaning operations necessary and further reduces the efficiency of this fabrication technique.
A method to thermally induce tensile stress for curvature adjustment of air-bearing surfaces is described in the U.S. Pat. No. 5,982,583. The patented method uses a laser beam to melt surface areas of the back face of the magnetic recording head. During the subsequent cooling process the melted material shrinks and induces a tensile strain energy on the back face, which bends concave. As a result, the whole structure of the magnetic recording head including the opposing air-bearing surface is deformed. This is a relatively expensive process, which requires individual slider measurement and repeated laser illumination. This process also produces debris, which must be cleaned from the sliders.
Therefore, there exists a need for a clean and efficient fabrication method that enables the formation of a curvature on a predetermined area of a solid structure like, for instance, an individual slider of a hard disk drive. The present invention addresses this need.